The present invention relates to a method of and apparatus for producing a multilayer ceramic board, and more particularly, to a method of and an apparatus for producing a multilayer ceramic board formed by stacking and thermally compression bonding green sheets having conductive wiring patterns for interconnecting a plurality of electronic devices and elements.
FIG. 7 is a flow chart illustrating an overview of the manufacturing process of the multilayer ceramic board formed by stacking and thermally compression bonding green sheets having conductive wiring patterns. In the initial stage of producing the multilayer ceramic board, a green sheet is made, then cut into a required shape and through-holes are formed thereon. Subsequently, a conductive wiring pattern is printed on the green sheet and a pressing for flattening can be conducted thereon. Then, a plurality of the above-mentioned green sheets are stacked and thermally compression bonded. After thermally compression bonding, the peripheral area of the green sheets are trimmed to form a predetermined shape, the green sheets are sintered at a predetermined temperature, a plating is applied to portions of the conductive wiring patterns and connectors, and finally LSI devices are mounted thereon. 1 As disclosed, for example, in a Japanese Utility Model Unexamined Publication No. 63-170232, a conventional apparatus for producing the multilayer ceramic board is known, wherein green sheets are stacked in a stack mold, then the mold is fixed by bolts and the sheets in the stacked state are thermally compression bonded and sintered.
However, in the conventional apparatus, there has been an unfavorable phenomenon that pressure on the peripheral edge portion of the green sheets becomes weaker than on other portions due to friction between the peripheral edge portion of the green sheets and inner wall surface of the stack mold. Namely, uniform pressure cannot be applied over the entire area of the green sheets.
When the above-mentioned phenomenon occurs, density becomes non-uniform over the entire area of the green sheets.. More specifically, as shown in FIG. 8, the density in the peripheral edge portion la and in the opposite surface 1b to the pressure applied surface 1c of the green sheets 1 becomes coarse; and the density in the center portion of the pressure applied surface 1c becomes fine.
When the green sheets 1 having the above-mentioned non-uniform density-distribution are stacked, thermally, compression bonded and then sintered, a difference in the sintering shrinkage rate along the thickness of the green sheets 1 occurs. As a result, a "camber" of the green sheets 1 is generated as shown in FIG. 10, since a relationship between the density and sintering shrinkage rate of the green sheets has a property in which the finer the density becomes, the lesser the level of the sintering shrinkage rate becomes as shown in FIG. 9.
The "camber" of the green sheets lowers dimensional accuracy of the conductive pattern and yield ratio in manufacturing and further results a rise of the manufacturing cost.